Electrical fuse



Jan. 26, 1943. H. A. TRlPLET-r 2,309,552

ELECTRICAL FUSE Original Filed Deo. 20, l1934 Patented Jan. 26, 1943 UNITED STATES PATENT OFFICE ELECTRICAL FUSE Hugh A. Triplett, Wilmette, Ill., assgnor to Schweitzer & Conrad, Inc., Chicago, Ill., a corporation of Delaware (Cl. Zoll-135) 2 Claims.

My invention relates, generally, to electrical fuses and it has particular relation to the construction of replaceable fuse links.

This application is a division of my copending application, Serial No. 758,372, filed December 20, 1934, and assigned to the assignee of this application.

The object of my invention, generally stated, is to provide a replaceable spring type fuse link that shall be simple and elicient in operation and which may be readily and economically manuiactured and installed.

An important object of my invention is to provide a relatively long length of silver fuse wire for interconnecting a pair of relatively closely spaced iniusible terminals of a replaceable spring type fuse link and, at the same time relieve the iuse wire of the spring stressA Another important object of my invention is to provide for relieving the stress that would otherwise be applied to the fusible element by the spring of a spring type link which is bodily replaceable.

An object oi my invention is to coil a fuse wire about the strain Wire of a replaceable spring type fuse link.

Other objects of my invention will, in part, be obvious and in part appear hereinafter,

Accordingly, my invention is disclosed in the embodiments hereof shown in the accompanying drawing, and it comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereinafter set forth and the scope of the application oi Which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of my invention reference may be had to the following detailed description taken in connection with the accompanying drawing in which:

Figure 1 is a View, in side elevation, of my irnproved form of replaceable spring type fuse link;

Figure 2 is a longitudinal sectional View, at an enlarged scale, of the fuse link shown in Figure l and illustrating one embodiment of my invention; and

Figure 3 is a fragmentary sectional View, similar to Figure 2, and showing another embodiment of my invention.

Referring now particularly to Figure l of the drawing, it will be observed that the reference character I designates a replaceable fuse link. This fuse link is of the type that is capable of being used in connection with almost any of the fuse housings that are being sold at the present time. The application of this fuse link to the various types of fuse housings is fully described in the application, referred to hereinbefore, of which this application is a division. According- 1y, a detail description of the application of the replaceable fuse link I0 to various types of fuse housings will not be set forth herein.

The fuse link l0 is replaceable as a uni-t. It comprises a fuse tube II, preferably formed of fiber, and it is secured, as will be described hereinafter, at its upper end to a terminal, shown generally at I2. The terminal I2 provides for connecting the fuse link I0 to one line terminal. At its other end, the fuse link Il) is provided with a iiexible lead or conductor I3 to permit connection to the other line or circuit terminal. The lower end I4 of the iiexible lead I3 is tinned in order to prevent fraying of the strands forming it. Intermediate the ends of the flexible lead or conductor I3 a collar I5 is secured. The collar member I5 is generally tubular in shape and is slipped over the flexible lead I3 to the desired position. It is then flattened, as illustrated, onto the strands forming the iieXible lead I3 in order to securely hold it in place. At its lower end the collar member I5 is provided with an integrally formed conical wedging portion I6 to permit connection to certain types of fuse mountings. It will be understood that the replaceable fuse link l0 is ordinarily positioned in a fuse tube and at its upper terminal I2 is connected to one of the circuit terminals. Connection to the other circuit terminal may be provided either by engaging the conical wedging portion I5 in suitable contact means or by connection of the flexible lead I3 to suitable terminals, as desired.

In Figure 2 of the drawing, the details of construction of the fuse link Il) are more clearly illustrated. As there shown the upper fuse link terminal I2 is provided with a threaded stud I9 for threaded engagement with various types of fuse mountings. In order to accommodate other types of fuse mountings a flanged head 20 is screwed onto the threaded end I9. ln` order to accommodate other types of mounting a dished washer 2ly Figure l, may be provided underneath the flange of the head 20. It will be understood that the upper end of the fuse link terminal I2 may take diierent forms depending` upon the application in which it is to be used. This is more fully described in my copending application, mentioned hereinbefore, of which this application is a division.

The terminal I2 may be machined from a suit able rod such as a rod of brass or copper the initial diameter' of which is indicated by the flange 22 intermediate its ends. The upper end is reduced in diameter and threaded as indicated at I9. Just below the flange 22 a circumferential groove 23 is provided into which the upper end of the fiber fuse tube I I may be pinched as indicated at 24. By securing the upper end of the fuse tube II as indicated, relative longitudinal movement with the terminal I2 is prevented. In order to prevent relative turning between the terminal I2 and the fuse tube I I, the terminal l2 is provided with a knurled portion 25. When the upper end of the fuse tube II is pinched into the groove 23, the edges of the knurled portion 25 bite into the inner surface of the fuse tube I I and securely hold it in place.

The lower end of the fuse terminal I2 is provided with a reduced portion 25 having an axially drilled aperture therein for receiving the composite fusible element, shown generally at 2l. As indicated the composite fusible element 2l' comprises a strain wire 28 and a fuse wire 2S. The strain wire 28 is preferably formed of high tensile strength wire, such as nickel-chromium wire while the fusible element 29 is preferably formed of silver. In this embodiment of the invention it will be observed that the sliver fuse wire 29 is wrapped in an open spiral about the strain wire 28.

The composite fusible element 2l comprising the strain wire 23 and the fuse wire 29 are inserted in the axially drilled aperture in the lower reduced portion 26 of the terminal I2 and then it is deformed onto them. This is done by fiattening the opposite sides to provide the construction shown. In order to further provide engagement between the strain and fuse wires 28 and 2:'1, the lattened portion 26 is locally deformed, as indicated at 38, by a suitable tool, such as a punch, so that the strain and fuse wires are securely held in place.

At its lower end the composite fusible element 27 is secured in the upper end portion 33 of a lower fuse terminal, shown generally at 34. The termina Si. is initially generally tubular in shape and is adapted to receive the lower ends of the strain and fuse wires 28 and 29. The upper end portion 33 is flattened onto the ends of the strain and fuse wires therein and is further locally deformed, as indicated at 35, for securely holding them in position. It will be understood that the deforming of the terminal portions 2G and 33 onto the ends of the strain and fuse wires 28 and 29 and then the locally deforming of them, as indicated at 3! and 35, not only provides for securing these wires in position but also insures good electrical connection thereto. This is important in fuse link construction.

The lower end 35 of the lower fuse terminal 34 is ilattened onto the upper end of the portion 3l of the ilexible lead I3 which extends into the fuse tube l I. It will be observed that the portion t is flattened substantially at right angles to the upper portion This construction facilitates the connection of the coil tension spring 38, the upper convolutions of which surround the portion 35 and the extreme upper convolution being reduced about the shoulders formed at the juncture with the upper portion 33.

The lower fuse terminal 34 is formed of copper or brass. Since the portions 2E and 33 of the fuse terminals I2 and 34, respectively, adjacent the composite fusible element 2'I comprising the strain wire 28 and fuse wire 28, are relatively massive as compared to the fusible element 2'I, they may be considered as being relatively infusible. When the fuse link is called upon to operate for the purpose of opening the circuit on the occurrence of a fault, only fuse wire 23 and the strain wire 28 are melted in the order named. The arc that is then formed is confined between the portions 25 and 33 of the terminals I2 and 34. Since they are relatively infusible little, if any, metal from them is vaporized by the heat of the arc with the result that the likelihood of the formation of a metallic vapor path for sustaining the arc is appreciably reduced. This is particularly true when the strands of the flexible lead I3 are taken into consideration. If the strain and fusible wires 28 and 29 were secured directly to the upper end of the section 3`I of the flexible lead I3 which extends into the fuse tube II', it is quite likely that considerable portions thereof would be vaporized due to the heat of the arc. This condition is obviated by the provision of a deinite metallic barrier between the fusible element 2'! and the flexible lead I3. As indicated, this is provided by the lower fuse terminal 34 which is relatively massive and relatively infusible.

As indicated hcreinoefore a coil tension spring 3S is provided and its upper end is attached to the lower fuse terminal 34. The spring 38 is .rovided for separating the terminal 34 from the terminal I2 when the fusible element 2'I blows. It is arranged to apply a predetermined tension to the fusible element 27. Since the str in element 28 provides a direct mechanical connection between the fuse link terminals I2 and 34 while the fuse wire 28 is coiled about the strain wire 28, the latter is relieved of any mechanical stress which would otherwise be imposed by the spring 38. At the same time a relatively long length of fuse wire 29 is provided between the closely spaced terminals I2 and 34 as will be readily apparent. Such length of fuse wire is desirable in order to provide the desired time-current fusing characteristics of the fusible element 21.

At its lower end the spring 38 is secured to a collar 39 that is flattened onto the lower end of the portion S1 of the flexible lead I3. It will be observed that the lower end of the fuse tube II is closed by an anchor plate 40 having a centrally located aperture 4I through which the flexible conductor I3 projects. The upper end of the collar member I5 abuts the under surface of the anchor plate 43 and thereby resists the stress imposed by the coil spring 38. It will be observed that the spring 38 does not apply any tension to the portion 3l of the flexible conductor I3 between the fuse terminal 34 and the collar 39. Any desired tension may be applied to the ilexible lead I3 externally, either by springs in the housing or by the lineman in refusing the housing, without imposing on the strain wire 28 any stress in addition to that already imposed by the spring 38 unless this stress imposed by the spring 38 is exceeded. This type of spring arrangement and fastening therefor provides a non-cumulative type of replaceable spring link. It constitutes a distinct advance in the art. However, the non-cumulative arrangement of the spring 38 forms no part of my invention. It is disclosed and claimed in the copending application of Lindell, Serial No. 70,230, illed March 23, 1936, and assivned to the assignee of this application.

In Figure 3 of the drawing I have illustrated a replaceable type of spring llnk that is generally similar to the link shown in Figures 1 and 2 of the drawing and described hereinbefore. The diierence resides in the construction of the composite fusible element 21'. As illustrated, the fuse wire 29', preferably formed of silver, is coiled in an open spiral about the strain wire 28 but, in this embodiment, the convolutions are spaced from the strain wire 28 rather than being in close engagement therewith as is the case with the fuse wire 29 as shown in Figure 2. When the fuse wire 29 is spaced away from the strain Wire 28, its time-current characteristic can be more accurately predetermined than is the case with a construction shown in Figure 2 since no heat generated therein is conducted therefrom directly by the strain Wire 28.

When the fuse wire 29 is spaced from the strain wire 28 it serves another useful function. Because of the relatively large effective diameter of the coil 29 as compared to the diameter of the strain wire 28 the effects of corona are materially reduced.

Since certain further changes may be made in the above constructions and different embodiments of the invention may be made without departing from the scope thereof, it is intended that all matters contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

l. A fuse link comprising, a pair of terminals, a fusible elementI in the form of a Wire connecting said terminals, a strain wire also interconnecting said terminals, said fusible element being wound upon the strain wire in definite contact with the same, a sleeve of insulation enclosing said element and wire, and a spring carried by the link, said spring being normally under stress tending to separate said terminals.

2. A fuse link comprising, a pair of terminals, a fmible element in the form of a wire connecting said terminals, a strain element also interconnecting said terminals, said fusible element `being wound in denite contact engagement around said strain element, and a sleeve of insulation enclosing said fusible and strain elements.

HUGH A. TRIPLETT. 

